Since the introduction of the first computer networks and in particular with the advent of the internet, voice communication over computer data networks has been a subject of interest. One of the major challenges of real time communication over data packet networks is to ensure that the data packets are delivered in sequential order.
Technology for transmitting voice conversations over the internet has been available to end users since at least the 1990's, and is generally called after its communication protocol Voice over Internet Protocol or VoIP. VoIP is operated as a client-server model.
At the start of VoIP, voice communication was limited to users of the internet. No connection to the POTS (Plain Old Telephony Services) system was offered. Some telecommunication equipment manufacturers offered “dual mode” telephone sets capable of delivering mobile VoIP.
Other communication protocols developed for voice communication over the internet by computers operate on a peer-to-peer model, rather than the more traditional client-server model. A user directory of these internet communication systems is substantially decentralized and distributed among the nodes in the network, which means that these networks can scale very easily to large sizes without a complex and costly centralized infrastructure.
Telephone calls between users of an internet communication system are in general free of charge, apart from a fee to an Internet Service Provider (ISP). To contact users outside the internet communication system, a subscription is available for internet users for placing calls to traditional telephone devices, including mobile telephones, for a fee. Internet users may also subscribe to receive calls on their computers or internet connected telephones, dialled by regular telephone subscribers to a local telephone number through which access to a user of the internet communication system is provided. A user of the internet communication system in Australia, for example, may subscribe to a local telephone number in Finland. Callers of Finland would only pay local or national rates to call that number.
Telecommunication operators and consumers have invested substantially in mobile telephone equipment. In developed countries, mobile telephones have achieved nearly complete market penetration, and many people are giving up landlines and using mobile equipment exclusively. On the other hand, due to the possibility of making phone calls free of charge, internet communication systems have gained increased interest of the public.
In view of these developments, there is a growing need for users of mobile communication systems and users of internet communication systems to contact each other while keeping the best of both worlds, i.e. mobility and ease of use of a mobile telephone and establishing and receiving calls as a regular internet communication user, respectively.
Most, if not all, of commercially available products may require hardware to be installed at home, may require the use of an additional SIM (Subscriber Identity Module) card or may require that hardware is connected to a Personal Computer (PC) which permanently needs to be switched on for establishing the required communication.
US patent application 2001/0034224 (McDowell et al.), discloses a system and method for sharing user event information among wireless devices and those connected to fixed IP networks, such as the Internet. Mobile user event information is to be understood as to mean information regarding the presence of a wireless or mobile device on its associated network. This event information is provided to the users of the IP network by a Mobile Event Server (MES) connecting to the mobile network and the IP network. The MES broadcasts event information to instant messaging services which in turn send the appropriate notification to instant messaging subscribers.
The instant messaging communication disclosed is a notification system and method, notifying subscribers of the presence of a wireless or mobile device such that a user in the IP network can send messages or place calls to the wireless or mobile user with a high level of confidence that the messages are being received in near real time.
An article by Liao, et al., “VoIP Mobility in IP/Cellular Network Internetworking”, elaborates on call set-up procedures between users of an IP network and cellular or mobile users. In particular, the applicability of H.323 signalling for supporting call establishment between an IP network user and a roaming cellular network user is discussed.
It appears that existing H.323 signalling is inadequate to cope with roaming mobile users. As a solution to this problem, the authors of this publication discuss to store in the HLR/VLR of the mobile user gateway identification associated with a registered mobile terminal. From this gateway identification information can be derived whether a mobile terminal is roaming from the location area associated with a different gateway, and hence to launch a handoff, if necessary.
U.S. Pat. No. 6,636,504 (Verizon Services Corp.), provides an arrangement for enabling reverse billing for Internet telephony calls. Reverse billing is to be understood that a called subscriber is charged for the costs of a telephone call between Internet and Plain Old Telephone Service (POTS) subscribers, for example.